REAPER script: Move all project markers by the same amount in seconds

-- Move all project markers by the same amount in seconds

local retval, num_markers, _ = reaper.CountProjectMarkers(0)
    if num_markers == 0 then reaper.MB("No markers in the project.","Error",0) return end

local retval, value = reaper.GetUserInputs("Move all markers by..", 1, "Format = sec.ms", "")
    if not retval or value == "" then return end
    local value = value:match("(%-?%d*%.?%d*)")
    if not value then reaper.MB("Illegal entry.","Error",0) return end

-- Save all project markers IDs
local i = 0
local t = {}
    while i < num_markers do
    local retval, _, pos, _, name, id = reaper.EnumProjectMarkers2(0, i)
    t[id] = pos + value
    i = i + 1
    end

reaper.Undo_BeginBlock()

-- Move all saved project markers
    for k,v in pairs(t) do
    reaper.SetProjectMarker2(0, k, false, v, 0, "")
    i = i + 1
    end

-- Done in stages since setting marker in the same loop as enumeration messes up their order while they're being moved

reaper.Undo_EndBlock('Move all project markers by '..value..' sec',-1)